Mobile chassis for carrying a tower crane

ABSTRACT

A traveling crane is provided with three bogies, one front and two rear, to provide for the support and transport of the crane. Support arms having retractable jacks are pivoted to the base of the crane to provide additional stabilizing support on opposite sides of the front bogie. The rear bogies may be mounted at opposite ends of a transverse beam or may be mounted on the free ends of two pivoted arms. In either case, the bogies are connected by means of a pivoted lever arrangement to provide for leveling of the chassis. The bogies may be provided with endless tracks or wheels.

I United States Patent 1151 3,638,805 Garnier 1 Feb. 1, 1972 [54] MOBILE CHASSIS FOR CARRYING A 2,422,210 6/1947 Reischl ..254/93 TOWER CRANE 3,191,954 6/1965 Schuetz....

3,236,535 2/1966 Barber 1 Aria, France 3,362,544 1/1968 Wellnitz ..212/14s x [73] Ass1gnee: 33111: Chevilly Larue (Val de Marne), FOREIGN PATENTS OR APPLICATIONS 1,022,267 3/1966 Great Britain ..212/145 [22] 1969 1,120,220 7/1968 Great Britain ..212/38 [21] Appl. No.1 858,691

Primary Examiner-Richard .1. Johnson Foreign Application Priority Data AnorneySughruc, Rothwell, Mron, Zinn & Macpeak Sept. 19, 1968 France ..50404 [57] ABSTRACT A traveling crane is provided with three bogies, one front and [52] US. Cl. ..212/38, 2 1 2/145, two rear to provide for the Support and transport of he Crane [511 Int. Cl. ..B60s 9/12, 862d 61/08 35" gi d 1 1??? P' t base [58] FieldofSearch ..l80/9.2, 9.52, 9.28,9.3,9.46, F e 3 S3 80/41 954 2l2/l45 254/93 86 280/61 posite sides of the front bogle. The rear bogies may be H 6 150 mounted at opposite ends of a transverse beam or may be mounted on the free ends of two pivoted arms. In either case, the bogies are connected by means of a pivoted lever arrange- [56] References Cited ment to provide for leveling of the chassis. The bogies may be UNITED STATES PATENTS provided with endless tracks or wheels.

2,268,017 12/1941 Busick ..280/6.1 4 Claims, 34 Drawing Figures 17 1s 11 l l Hill 10 9 l 11 111+ l l l lllll PATENTED FEB I m2 SHEET OlUF 1O lIHl HHH ll PATENTEDFEB 1m 3,638,805 SHEET OEUF 10 PATENTEUFEB sum user 10 PATENTED FEB 11972 3.638.805 SHEET DMF 10 PATENTEDFEB 11972 3.638.805 SHEET OSOF 70 PAIENIEWB mzz $638,805 SHEET 080? 10 PATENTED FEB 1 i972 SHEET 070F 10 PATENTEU FEB 1 I972 SHEET 08UF 10 PATENTED FEB 1 I972 SHEET IOUF 10 MOBILE CHASSIS FOR CARRYING A TOWER CRANE The present invention relates to a mobile chassis intended to carry a tower crane, this chassis being either self-propelled or drawn. The invention principally concerns the construction of the carrying and controlling assembly as well as the means with which it is provided to carry out the transportation and the site erection of tower cranes which may be rapidly dismantled.

It is known that up to the present, the majority of tower cranes, notably those of high capacity, are mounted on components at the site and placed on rails for displacing movement. The cost ofinstalling the track is very high, as is the cost of the crane assembling and dismantling operations.

The present invention has the aim of avoiding these disadvantages by dispensing with the installation of tracks and reducing the time or erection of the crane on the site. In addition, it allows the assembly to be moved for short distances, even on sloping ground, without having to fold up the crane.

A crane chassis according to the invention is mainly noteworthy in that it comprises a base fitted at the front with a running gear either of wheels or endless tracks mounted on a ball joint, and, at the rear, with two sets of running gear each carried on its own telescopic hydraulic system, as well as with two lateral arms situated one on each side of the base between the front and rear running gear, each of these arms pivoting around a vertical axis and carrying, at its free end, a shoe to bear on the ground controlled by a hydraulic jack. All the running gears are detachable, and notably the rear running gears may be replaced by wheels with pneumatic tires allowing transport on the road.

Following a first possible manufacturing method for the invention, the three running gears each comprise an endless track, at least one of which is adapted to drive by electric or hydraulic means.

Following another possible manufacturing method, the three running gears are constituted at the rear by two articulated bogies with several tired wheels, and at the front by a driving and steering bridge mounted on a balance beam.

In either of these two variants, the two rear running gears may be either mounted at the two ends ofa fixed erosspiece of the chassis base, or arranged each one at the rear end of a swinging arm pivoted by a vertical shaft to this same base.

In all cases the mounting of the shoes of the stabilizing arms on jacks allows these arms to be used not only to maintain the crane in its place of working, but also to raise either the front or the rear of the chassis in order to fit or to remove tired wheels intended for road transport. In order to carry out this action on the front rolling gear, the two stabilizing arms are lowered towards the front; on the contrary, they are brought towards the rear if it is desired to raise this part of the chassis in order to fit or to remove the rear running gear.

A crane chassis according to the invention, together with modifications, will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a view in elevation ofa chassis according to the invention, which is mounted on endless tracks and carries an extended crane, the stabilizing arms not being shown for clarity in the drawing,

FIG. 2 is a corresponding plan view, showing the stabilizing arms extended,

FIG. 3 corresponds to FIG. 1 showing the arrangement when the extended crane is moving on sloping ground,

FIG. 4 is a similar front view,

FIG. 5 shows the position of the stabilizing arms, the shoes of which are raised while the crane is moved,

FIG. 6 is a corresponding plan view showing schematically the support polygon of the assembly when the shoes ofthe stabilizing arm are raised,

FIG, 7 corresponds to FIG. 5 after the stabilizing shoes are lowered on to the ground,

FIG. 8 is a plan view showing the support polygon thus obtained,

FIGS. 9 to 14 show the successive phases of the operation of attaching the chassis according to the invention behind a road tractor intended to transport the chassis in the fashion of a semitrailer,

FIG. 15 is a plan view ofa variant intended to allow a lateral movement of the chassis,

FIG. 16 is a plan view of another possible manufacturing variant of a chassis according to the invention, in which the rear endless tracks are mounted on two swinging arms,

FIGS. 17, 18 and 19 illustrate the successive phases of putting the chassis of FIG. 16 on to the road.

FIG. 20 is a plan view of an extra variant ofa chassis according to the invention, in which the running gears are constituted by tired wheels,

FIG. 21 is an elevation in part section of one of the bogies carrying the rear wheels,

FIG. 22 is a corresponding plan view,

FIG. 23 is a lateral section of this same bogy,

FIG. 24 shows a possible method of construction of the latching system of the rear arms in the position for movement on the site,

FIG. 25 is a similar view to FIG. 24 when the arm is aligned in the axis of the chassis for the position for road transport,

FIGS. 26 and 27 show the successive phases of the operation of attaching this variant behind a road transport tractor,

FIGS. 28, 29 and 30 show a variant in which the crane on pneumatic tires is self-propelling,

FIG. 31 shows, in order to show the disadvantages, what would be the mounting of the rear endless tracks on a known system of telescoping,

FIG. 32 shows another known system of telescoping,

FIG. 33 shows, on the contrary, the system of telescoping used according to the invention, with its particular advantages,

FIG. 34 illustrates the kinematics ofthe device according to the invention, showing the arrangement of two extreme positions.

The chassis shown in FIGS, 1 to 14 comprises a horizontal base 1 fitted with a rear crossbeam 2. The crane proper, formed by a mast 3 and ajib 4, is fitted to a revolving pedestal 5 carried by a directional sprocket wheel 6 placed in the center of the base 1.

At the front the base 1 of the chassis carries a balljoint 7 which bears on a endless track assembly formed by a block 8 and two tracks 9. The block 8 encloses known driving methods, hydraulic or electric, not shown, which enable the endless track assembly 8-9 to propel the chassis. In addition, this track assembly can steer, since it is linked to the base I by the balljoint 7.

The crossbeam 2 is preferably linked to the base 1 by pegging or by means of bolts, which will allow rapid dismantling. At each end of the crossbeam 2 is mounted supporting endless track gear comprising a block 10 placed between two tracks 11 (FIG. 2). Each endless track assembly 10-11 is linked to the corresponding end of the crossbeam 2 by a raising system linked by a connecting arm 12 and a jack 13, of the kind shown in FIG. 33, 30 and 31. For simplicity in the drawing, such a raising mechanism which allows the position of each track assembly 10-11 to be varied in height in relation to the crossbeam 2, has been designated by the global reference 14.

At the level of the connection of the base 1 with the mast 3 of the crane, there are provided two vertical pivoting shafts l5 placed one on each side of the sprocket wheel 6. On each shaft 15 a stabilizing arm 16 is pivoted its free end carrying a vertical jack 17 fitted at its lower end with a shoe 18 for bearing on the ground.

Some detachable connecting arms 19 and 20, pivoted at their two ends, allow the locking of the orientation of the rear track assemblies 10-11 and of the stabilizing arms 16 respectively, in relation to the chassis 1-2.

On the base 1, there is mounted a hydraulic control center, not shown, for the control of the driving endless track gear 9, as well as for operating the stabilizing jacks l7 and the raising jacks 13 of the supporting mechanisms 14. The controls of these different services are grouped on the side of the chassis in such a way as to be readily accessible.

The operation and the advantages of such an arrangement are as follows:

The combination which has just been described constitutes an original self-propelled assembly which allows particular operations to be carried out:

a. The crane 3,4 may be moved while remaining extended, benefiting from a large triangular support polygon 21 (FIG. 6). During these movements, the jacks 17 are contracted and the shoes 18 raised above the ground (FIG. On the other hand, the stabilizing arms 16 are pegged in position, ready for chocking, carrying the raised shoes 18.

The fact of mounting the front track assembly 8,9 on a ball joint allows it to adapted itself to uneven ground whilst allowing it to steer the machine assembly, according to whether the one or the other of the tracks 9 is braked. The directional control of the self-propelled chassis according to the invention is thus ensured.

The rear track assemblies 11 are designed in such a way as to be able to move independently in height, due to the mechanisms 14. This allows the base 1 to be kept constantly horizontal, whatever the slope of the ground, longitudinally (FIG. 3) or in the transverse direction (FIG. 4).

The rear track assemblies 10, 11 are also connected by ball joints to the crossbeam 2, in order to accommodate themselves to any form of ground. On the other hand, the reaction connecting rods 19 attach them to the chassis to hold them in a position parallel to the longitudinal axis of the machine as a whole.

b. The machine may be immobilized in its workplace by holding the base 1 in a perfectly horizontal position in all cases (FIGS. 7 and 8). For this, an adjustment is made in the height of the jacks 17 of the two shoes 18 bearing on the ground, and of the jacks 13 of the rear suspension mechanism 14. Since the control of these four jacks are independent, it will be understood that this chocking operation is almost instantaneous. The four bearing points on the ground are constituted by two shoes 18 and two track assemblies 10, 11 so that the crane has then available a large rectangular support polygon 22. The axis of the crane mast 3 and of the sprocket-wheel 6 is situated in practice in the middle of this rectangular polygon 22.

As has already been indicated, one of the essential objects of the invention derives from the fact that the times of installation and of setting up for transportation are very short, the operations necessary for this work being particularly simple. in fact, given that such a machine eliminates all the work of preparing the ground and of installing rails, it would be unthinkable for the time and money thus gained to be partially lost by having a long setting-up time. In addition, the crane 3, 4 being preferably of a rapid fixing type, it is necessary to retain rapid setting up for the whole unit. All this is particularly well illustrated by the process of dismantling which will now be described, to pass from the working position to the road position (FIGS. 9 to 14).

In the commencing position, the jib 4 and the mast 3 are folded horizontally on the base 1 (FIG. 9). The machine is normally checked on the ground.

In a first phase, (FIG. 9) a towing beam 23 is fixed to the front of the platform 5.

In the following phase, the front track assembly 8,9 is disconnected (FIG. 10) by lowering the stabilizing shoes 18 to bear on the ground and allow the front of the chassis to be raised. This front track assembly 8, 9 is then dismantled, by means of the rapid unpegging with the help of a known auxiliary handling machine not shown.

The front track assembly having been taken away (FIG. 11), a road tractor 24 is brought up and reversed to bring its saddle 25 under the beam 23. By contracting the jacks 17, the front of the chassis is lowered along with the beam 23, which comes to a suitable height to be hooked on to the saddle 25.

By contracting the jacks 17, the shoes 18 are raised, which allows the stabilizing arms 16 to be brought towards the rear, by pivoting in the direction of the arrows 26 (FIG. 12). The linking connecting rods 20 are latched to the rear of the base 1 to immobilize the arms 16 in this position. By again expanding the jacks 17, the shoes 18 are lowered to bear on the ground, then the rear of the chassis is raised, notably the two rear track assemblies 10, 11 which lose contact with the ground (FIG. 13). It would also be possible if needs be to obtain the same result by the simple contraction of the jacks 13 of the raising mechanisms 14, if the initial position of the track assemblies 10, 11 allows it.

With the help of the auxiliary handling machine, not shown, which has already been mentioned, the two rear track assemblies 10, 11 are dismantled, then the crossbeam 2 which is freed by the rapid unpegging mechanism. Then a set of bogies 27 mounted on tired wheels 28 is brought under the mast gear (FIG. 14), then the rear of the chassis is lowered by raising the stabilizing shoes 18 so as to bring the coupling components of the body 27 in line with those fitted to the rear of the pedestal 5. This bogy 27 and the pedestal 5 are joined together, then the stabilizing shoes 18 are raised completely and the pivoting arms 16 are brought against the rear of the base 1, where they are locked.

In this way, the tractor vehicle 24 can transport the crane on the road like a semitrailer.

When the assembly reaches a new site, the setting up of the crane is carried out by a reverse process.

There is shown in FIG. 15 a first possible variant designed to allow the assembly to move laterally on the site. This has, among others, the advantage of avoiding steering maneuvers which require a fairly large working area. This likewise allows the crane to draw back or to advance without its having to be maneuvered, whatever may be its starting position.

The originality of this variant consists in being able to fix the direction of the front and rear tracks with respect to the axis of the chassis. In the case of FIG. 15, it has been supposed that this direction was perpendicular to the axis of the chassis, but it is evident that one could also choose a different angle. In order to obtain this result, it is necessary to make to drive not only the front track assembly 8, 9 but also one of the two rear track assemblies l0, 11. The linear speed of the front and rear tracks 9 and 11 must be identical.

In order to fix the direction of the track assemblies, it is possible slightly to raise the front of the chassis by lowering the stabilizing shoes of the arms 16 which are brought forwards (FIG. 15), then to set the direction of the front track assembly 8, 9 manually and to keep it in place by means of a coupling brace 29. Then the shoes 18 are raised, the arms 16 are brought rearwards (arrows 26), the shoes 18 are again lowered and the rear of the chassis and the track assemblies 10, 11 are raised by means of the jacks 17. These track assemblies have their direction set by hand and they are immobilized by coupling braces 30.

In order to avoid the manual direction-setting operations of the track assemblies, the braces 29 and 30 may be replaced by jacks which remain in place. In addition, if these jacks are sufficiently powerful, the operation of raising the chassis may be avoided and the direction of the track assemblies 8, 9 and 10, 11 may be set while they remain on the ground.

There is shown in FIGS. 16 to 19 another constructional variant in which the rear of the base 1 is no longer attached to a crossbeam 2, but it fitted with two swinging arms 31 opposite to the stabilizing arms 16 and fixed symmetrical to them. Each arm 31 is pivoted on a vertical shaft 32 carried by the rear of the base 1. At its opposite end, it supports the corresponding rear track assembly 10, 11. As previously, the mounting of each track assembly 10, 11 on its arm 31 is carried out by a suspension and raising mechanism 14. Detachable connecting rods 33 link the arms 31 to the base 1 and hold them in position.

It will be seen in FIG. 16 that this arrangement does not change the area of the triangular support polygon 21 or the rectangular polygon 22 according to whether the shoes 18 are raised in the movement position (lower half of FIG. 16) or lowered in the chocking position (upper half of FIG. 16). In addition, this variant with two arms 31 is able to be adapted to the mounting as in FIG. 15, that is to say allowing the track assemblies 8, 9 and 10, 11 a direction perpendicular to the longitudinal axis 34 of the chassis.

FIGS. 17, 18 and 19 illustrate the operation to bring this variant to the road transport position.

The dismantling of the front track assembly 3, 9 and the coupling of the beam 23 to the saddle of the tractor 24 is carried out as previously. From this position (FIG. 17) the stabilizing arms 16 are brought backwards (arrows 26) and their shoes 18 are lowered to the ground so as to raise the rear of the chassis including the arms 31 and the track assemblies 10, 11. These latter may then be dismantled, then the arms 31 are pivoted backwards (arrows 35, FIG. 18) to bring them in line with the chassis assembly. They are held in this position by appropriate locking ofthe connecting rods 33.

Then a double set of bogies 36 is brought under the arms 31 where it is rapidly fixed by some known system. Finally the stabilizing shoes 18 are raised and the arms 16 are brought forward where they are pegged against the chassis. The assembly is thus prepared for road transport like a semitailer.

The interest of such construction lies in the fact that the main beam 37 of the chassis is shortened and the detachable crossbeam 2, which must be specially transported in the case of FIGS. 1 to 15, is eliminated.

There is shown in FIGS. to 27 another possible constructional variant in which the sets of tracks have been replaced by sets of tired wheels. Such a design loses the advantage of the sets of tracks (the possibility of movement over any ground, the reduction of the pressure on the ground, the possibility of keeping the crane vertical during movement), but it is, on the other hand, of undeniable interest in the rapidity of setting up on the site, for altering to the transport position, and finally regarding the simplification of construction of the chassis.

It is important to note that the two possible conceptions, with tracks or with tires, have very different uses, so that it cannot be claimed that one is better than the other. In fact, the track gears are designed for a machine for use on any ground, whilst if the machine is needed to move only on prepared ground, relatively flat and without excessive slope, the sets of tired wheels give complete satisfaction.

The chassis shown in FIGS. 20 to 27 is similar to that of the variant shown in FIGS. 16 to 19. The front track assembly is replaced by a driving and steering bridge 37 fitted with two tired wheels 38. This bridge 37 is mounted on a balance beam, in a known arrangement, which allows it to encompass all variations in ground. It may be driven by any known propulsion system, for example, by hydraulic or electric motor or by a heat engine. A hydraulic jack, not shown, ensures directional control of the wheels 38.

The rear track assemblies are replaced by a bogy 39 mounted on the end of each arm 31. Each body 39 comprises a balance beam 44, pivoted at its center on a shaft 40 to accommodate variations in the ground, and it carries two tired wheels 41. In addition, still at the end of each arm 31, there is mounted a vertical jack 42 fitted in its lower part with a shoe 43. By expanding the jack 42, this shoe 43 is applied against the ground, which allows the machine to be chocked in its working position.

In the example shown in FIGS. 21, 22 and 23, it has been supposed in addition that each bogy 39 may have its direction adjustable in relation to its arm 31, about a vertical axis 45 coincident with that of the jack 42. In this way, the bogies 39 remain in a direction parallel to the longitudinal axis 34 of the chassis.

Given that the rear arms 31 may have their direction varied, there are illustrated by way of a nonlimiting example in FIGS. 24 and 25, a device which allows each bogy to be held in the desired position. In FIG. 24 the arm 31 is unfolded in the position for movement over the ground. A bolt or locking peg 46 holds the top 47 of the bogy 39 in the required position.

On the other hand, if the arm 31 is aligned in the axis of the chassis for the transport position, the locking system 48 is used to hold the top 47 of the bogy 39 in the same direction (FIG. 25). The bolt or peg 36 is fitted for this purpose in a slotted opening 48 in the top 47 of the bogy 39, and it likewise passes through a slotted opening 49 in a plate 50 attached to the arm 31.

For the change from the site position (FIG. 20) to the transfer position (FIG. 25), the process is very much akin to that which has been described for FIGS. 16 to 19. Instead of removing the front bridge 37, it is sufficient simply to remove the wheels 38 to achieve sufficient ground clearance. This operation is carried out after having raised the front of the chassis by means of the stabilizing shoes 18, the arms 16 being brought forward as shown in FIG. 20. Then the tractor 24 is coupled in the way already described.

To continue the operation, the stabilizing arms 16 are brought towards the rear (arrows 26, FIG. 26), their shoes 18 are lowered in order to raise the arms 31, then the bogies 39 are turned on their pivots 42, since they are no longer in contact with the ground. Each of these is fixed parallel to its arm 31.

Then the arms 31 are swung towards the rear to align them parallel to the chassis assembly (FIG. 27) to which they are attached by means of locking braces 33 and 51, so as to form a rigid assembly. The stabilizing shoes 18 are raised, then the arms 16 are brought against the front beam 37 of the chassis, where they are locked. The machine is ready for transport (FIG. 27). It will be seen that the tandems or rear bogies 39 are used to move the erected crane (FIG. 20) as well as to transport it on the road (FIG. 27), and this without any dismantling.

A supplementary possibility may be added to the version on tires which has just been described (FIGS. 28, 29 and 30). In this case, there is shown a crane which is self-propelling both on the site and on the road, which makes it totally independent and avoids the use of a tractor, while simplifying the setting to the road or the site position. For this, it is sufficient to equip the chassis 1, 37 with a propulsion unit 75. This unit comprises, for example, a heat engine followed by a traditional drive of a road vehicle, or else with a hydraulic unit or electric motors.

In addition, a driving position or seat 76 is fitted to the chassis 37, for example at the front, to allow the machine to be driven on the road.

This steering position 76 and the propulsion unit 75 may be detachable, which allows the machine to be dual purpose, that is to say, to be either self-propelling (FIGS. 28, 29 and 30), or drawn as in the case of FIGS. 20 to 27.

In FIG. 28 there is shown a plan view of the machine in the working position. The same references have been retained to designate the components corresponding to those of FIGS. 20 to 27. It will be noticed in FIG. 28 that the stabilizing arms 16 have been supposed to be telescopic.

FIG. 29 shows the self-propelled crane folded in the position for road transport. The telescopic arms 16 are contracted and brought towards the front. As previously, locking brackets 51 and 33 ensure the rigidity of the two rear arms 31.

FIG. 30 shows in elevation the self-propelled crane folded in the road position. The position of the rear propulsion unit 75, placed between the carrying arms 31 of the bogies and the location of the steering position 76 at the front of the chassis 37, will be noticed.

According to requirement, various distributions of the driving wheels may be provided, namely:

either a traction unit constituted by the driving and steering bridge of the wheels 38;

or driving wheels 41 on the rear bogies 39,

or all the wheels 38 and 41 made to drive if the machine is intended to move over difficult ground.

With the machine in the working position on the site, (FIG. 28), its alteration to the road transport position (FIGS. 29 and 30) is carried out in a very simple manner. In fact, when the crank is folded, the stabilizing shoes 18 are first raised, then the arms 16 are brought rearwards as already shown on FIG. 26 by the arrow 26. By lowering the shoes 18, the bogies 39 are raised from the ground, they are aligned with their arms 31 (the case already shown for FIG. 26), and the arms 31 are brought into the longitudinal axis of the chassis, where they are retained by means of the braces 33 and 51 (FIG. 29). The stabilizing shoes 18 are raised again and the arms 16 are brought contracted towards the front and are latched on the chassis 37. The machine is then ready for road transport (FIGS. 29 and 30).

Mention has been made earlier of the rasing mechanisms 14 which link the rear track assemblies 10, 11 to the crossbeam 2 or to the arms 31. To carry out this function, it would have been possible to think of utilizing the known systems of the kind shown, for example in FIGS. 31 and 32. It will be seen why these systems would not have given satisfaction, and why, in the particular case of the invention, it was necessary to provide the mechanisms 14 shown schematically in FIGS. 33 and 34.

Following the known arrangement of FIG. 31, a simple vertical cylinder 52 would have been provided at each end of the crossbeam 2, a piston 53 sliding in this cylinder to act by a stem 54 on the block of the track assembly in question. Given that in these conditions the jack 52, 53, 54 is caused to work both in compression and bending to accommodate the lateral movements of the track assembly 10, 11 relative to the crossbeam 2, it is necessary to make this jack oversize, that is to say to increase the diameter of the stem 54 and the guided length of this stem. This amounts to considerable loss in the length of useful stroke 55. In addition, to this useful stroke there must be added the space 56 occupied by the end of the jack. Assuredly, this apparently simple construction occupies much space unusable for the displacement stroke, and it leads to oversize and extremely costly jacks.

To avoid this disadvantage, another known solution (FIG. 32) consists in using a jack 57, 58, S9 situated within a telescopic tube 60, 61 which has the sole purpose of absorbing the bending stresses and assuring guiding.

This solution has the advantage of allowing the use of a jack 57, 58, 59 of smaller capacity but, on the other hand, the diameter of the telescopic tube 60, 61 is relatively large, which necessitates a fairly large minimum guide length 62. Here again it is therefore necessary to encroach upon the useful stroke. Moreover, the method leads to costly machining for the telescopic tube 60, 61.

Neither of these two conventional systems (FIGS. 31 and 32) giving satisfaction, it has been necessary for carrying out the invention to design for the rear track assemblies 10, 11 the mechanisms 14 shown in FIGS. 33 and 34. Such a mechanism 14 is fitted at the end either of the crossbeam 2 or of an arm 31. It comprises a fixed shaft 63 on which is pivoted the bend of an elbowed crank arm 64. At one of its ends, this crank is linked by means ofa shaft 65 to the stem of the jack 13, which is in addition linked to a fixed shaft 66 on the arm 31 or the crossbeam 2. At its other end, the elbowed crank 64 is connected by means of a pivot shaft 67 to the center of the straight connecting rod 12 already mentioned. At its top this connecting rod 12 is linked by a shaft 68 to a second connecting rod 69 pivoting on a fixed shaft 70. The lower end of the connecting rod 12 carries a balljoint 71 connecting it with the block 10 of the rear track assembly 10, 11 in question.

The four pivots 63, 67, 68, 70 form the angles of a quadrilateral which in the intermediate position shown in FIG. 33 has approximately the shape ofa trapezium with a right angle. The large base of this deformable quadrilateral is constituted by the side 63, 67 while the pivots 70 and 68 define the small side. In addition, the side 67, 68 is very little inclined from the vertical, the direction of the connecting rod 12 tending to make its lower end 71 further from the center of the machine than its upper end 68.

All the interest of this system lies in the judicious positions of the shafts 63, 67, 68, 70 which are such that if any exterior force is exerted on the ball joint 71 through the track assembly 10, 11 whatever the direction of this force, the quadrilateral 63, 67, 68, 70 is deformed, whilst the ball joint 71 is moved in practice along a vertical axis 72 (FIG. 34) between an upper position 71a and a lower position 71b. This therefore maintains constant the distance between the axes of the two rear endless track assemblies 10, 11.

In addition there is shown schematically in FIG. 34 an intermediate position and 71c for the connecting rod 12 and the balljoint 71.

It will be understood that such a mechanism 14 principally allows:

a. to gain in useful stroke since there is no longer need to take account of a dead length for guiding the jacks,

b. to achieve a simple construction,

c. to use ajack 13 which works only in compression, so that it may be given dimensions according to the wishes of the manufacturer in varying the two parameters characterizing the operation of the elbowed crank 64, namely the force of thrust 73 and the length of the lever 74 (FIG. 33).

The preceding description has been given only by way of a nonlimiting example, the scope of the invention will not be exceeded by replacing the constructional details described by other equivalent arrangements.

lclaim:

1. A movable chassis for a tower crane comprising platform means having a front end and a rear end for supporting a tower crane, a single steerable running gear means pivotally secured to said front end, crossbeam means secured to the rear end of said platform means, two additional running gear means adjustably secured to each end of said beam means for vertical movement of said additional running gear means relative to said beam means, a pair of support arms pivotally secured to said platform means for pivotal movement to a position wherein the free ends of each of said arms will be disposed in alignment with and on opposite sides of said single running gear means and in alignment with a respective running gear means on each end of said beam means along lines parallel to the front-rear axis of said platform means, and vertically adjustable ground support means secured to the free end of each arm.

2. A mobile chassis as set forth in claim 1, wherein each running gear means is detachably secured to said platform means or said beam means, and further comprising pedestal means rotatably mounted on said platform means, coupling means detachably secured to said pedestal means for coupling the mobile chassis to a towing vehicle and transport means suitable for road travel detachabiy secured to said pedestal means.

3. A mobile chassis as set forth in claim 1, wherein each additional running gear means is linked to said beam means by a mechanism comprising a fixed shaft on which is pivoted the angle of an elbowed crank one end of which is linked to ajack which is pivoted on a fixed shaft on said beam means, the other end of the crank beam pivoted to the central part of a straight connecting arm, the lower end of which has a ball joint connecting said arm through a block of the running gear means, the upper end of said connecting arm beam pivoted to a second connecting arm which is pivoted on a fixed shaft on said beam means, the four pivots of the connecting arms and crank forming the angles of a quadrilateral figure which, in an intermediate position has approximately the shape of a trapezium containing a right angle so that when it is deform ed, the ball joint in practice moves along a vertical axis, thus keeping constant the distance between the axes of the two running gear assemblies.

4. A crane chassis according to claim 1, in which each of the said three running gears comprises an endless track assembly at least one such assembly being adapted to be driven by a mo- 10!. 

1. A movable chassis for a tower crane comprising platform means having a front end and a rear end for supporting a tower crane, a single steerable running gear means pivotally secured to said front end, crossbeam means secured to the Rear end of said platform means, two additional running gear means adjustably secured to each end of said beam means for vertical movement of said additional running gear means relative to said beam means, a pair of support arms pivotally secured to said platform means for pivotal movement to a position wherein the free ends of each of said arms will be disposed in alignment with and on opposite sides of said single running gear means and in alignment with a respective running gear means on each end of said beam means along lines parallel to the front-rear axis of said platform means, and vertically adjustable ground support means secured to the free end of each arm.
 2. A mobile chassis as set forth in claim 1, wherein each running gear means is detachably secured to said platform means or said beam means, and further comprising pedestal means rotatably mounted on said platform means, coupling means detachably secured to said pedestal means for coupling the mobile chassis to a towing vehicle and transport means suitable for road travel detachably secured to said pedestal means.
 3. A mobile chassis as set forth in claim 1, wherein each additional running gear means is linked to said beam means by a mechanism comprising a fixed shaft on which is pivoted the angle of an elbowed crank one end of which is linked to a jack which is pivoted on a fixed shaft on said beam means, the other end of the crank beam pivoted to the central part of a straight connecting arm, the lower end of which has a ball joint connecting said arm through a block of the running gear means, the upper end of said connecting arm beam pivoted to a second connecting arm which is pivoted on a fixed shaft on said beam means, the four pivots of the connecting arms and crank forming the angles of a quadrilateral figure which, in an intermediate position has approximately the shape of a trapezium containing a right angle so that when it is deformed, the ball joint in practice moves along a vertical axis, thus keeping constant the distance between the axes of the two running gear assemblies.
 4. A crane chassis according to claim 1, in which each of the said three running gears comprises an endless track assembly at least one such assembly being adapted to be driven by a motor. 